The present invention is related to methods of plasma treatment of polymer materials in order to modify the surface of these materials for improving the hydrophilic character of the surfaces, and to materials obtained by such methods. The plasma treatment involves an atmospheric pressure plasma.
A lot of polymers having a stable structure, which resists attack from various solvents, or from environmental conditions have the drawback of being poorly wettable. Surface wettability is however an interesting property for industrial applications. In the prior art, attempts have been made to modify the surface of such polymer materials by a plasma treatment.
WO 2009/037331 describes to apply a hydrophilic coating on a substrate by exposing the substrate to an atmospheric pressure plasma discharge in which an aerosol of a non-polymerizable acetate derivative, such as ethyl acetate, is introduced. Treatment of poly(ethylene terephtalate) with this method resulted in a reduction of the contact angle with water from 67° to 10° and for poly(propylene) a reduction from 98° to 10° was reported. The reduction is reported to be stable for several months.
US 2011/0060402 describes methods for surface modifying a hydrophobic polymer such as expanded poly tetrafluoroethylene (ePTFE) by pre-treating the hydrophobic polymer sequentially with low pressure (sub atmospheric) plasmas, dip coating the hydrophobic polymer material with a hydrophilic coating, e.g. polyethylene glycol (PEG) acrylate, and polymerizing the hydrophilic coating by exposure to a low pressure plasma.
CN 103263863 describes a method of improving the surface hydrophilicity of a polyether sulfone (PES) ultrafiltration membrane by treating the membrane using a low temperature plasma discharge, and by grafting an acrylic monomer on the plasma treated membrane in a vacuum oven. An increase of pure water flux of the membrane is reported.
The inventors have observed that in most cases the hydrophilic properties of the modified surface regressed with time, in particular when the surface is contacted with water.
An objective of aspects of the present invention is to provide an improved method of modifying the surface of a hydrophobic polymer. An objective of further aspects of the present invention is to provide a hydrophobic polymer material having a surface which is modified to have improved hydrophilic properties. It is an object to provide such methods and/or materials which provide improved stability of one or more hydrophilic properties when the surface is aged in water. It is also an object to provide such methods and/or materials which are easier to implement or manufacture and more cost effective.
According to a first aspect of the invention, there is therefore provided a method for enhancing hydrophilicity of a hydrophobic polymer material, as set out in the appended claims.
According to a second aspect of the invention, there is provided a substrate comprising, or consisting of a hydrophobic polymer material having a modified interface, as set out in the appended claims.
According to another aspect of the invention, which alternatively can be combined with any of the previous aspects of the invention, there is provided a method of plasma treating a hydrophobic polymer material, said method comprising arranging the hydrophobic polymer material on a porous support and applying suction pressure through the porous support during the plasma treating.